1. Field of the Invention
The present invention belongs to the field of pharmaceutical science, and provides an oral controlled release dosage formulation containing venlafaxine hydrochloride.
2. Description of the Related Art
Venlafaxine hydrochloride is described in U.S. Pat. Nos. 4,535,186; 4,761,501 and 6,342,533 which teach the production of venlafaxine and its analogues and are incorporated herein by reference. Venlafaxine hydrochloride is marketed as an antidepressant and for the treatment of Generalized Anxiety Disorder. Other uses include prevention of major depressive disorder relapse, bipolar and manic disorders, post traumatic stress disorder, late luteal phase dysphoric disorder, Gilles de la Tourette syndrome, bulimia nervosa or Shy Drager Syndrome, attention deficit disorder, Parkinson's disease, epilepsy, cerebral function disorders, obesity and weight gain, incontinence, dementia and related disorders. It is the preferred antidepressant where weight gain is problematic, as it is with the selective serotonin reuptake inhibitors (SSRIs). Venlafaxine hydrochloride is a phenylethylamine-derivative chemically unrelated to other currently available antidepressants (e.g., selective serotonin-reuptake inhibitors, tricyclics, tetracyclics). It is designated (R/S)-1 -[2-(dimethylamino)-1-(4-methoxyphenyl)ethyl] cyclohexanol hydrochloride and has the empirical formula C17H27NO2 HCL. Venlafaxine has a pKa of 9.4 and has a water solubility of 572 mg/mL.
The neurochemical mechanism of the antidepressant effect is believed to be potentiation of neurotransmitter activity in the central nervous system (CNS). Venlafaxine and its active metabolite, O-desmethylvenlafaxine (ODV), are potent inhibitors of neuronal serotonin and norepinephrine reuptake and weak inhibitors of dopamine reuptake. Venlafaxine does not inhibit monoamine oxidase and has no significant affinity for muscarinic, histaminergic or alpha-1 adrenergic receptors.
The drug is useful in the treatment of depressive affective disorders (e.g. major depression) at dosages of 37.5 to 375 mg daily (dosages exceeding 375 mg daily of extended release tablets are not recommended). The drug is available in both immediate-release tablets (EFFEXOR®) and extended-release capsules (EFFEXOR® XR). The sustained release capsules are available in 37.5, 75 and 150 mg capsules administered in a single dose either in the morning or in the evening at approximately the same time each day. If desired, patients with depression who are undergoing treatment with a therapeutic dose of conventional tablets may be switched to the extended-release capsules at the nearest equivalent daily venlafaxine dose (e.g., 37.5 mg twice daily to a 75 mg extended-release capsule once daily). To minimize gastrointestinal intolerance, it is recommended that the drug be taken with food. However, neither food nor time of administration has been found to effect bioavailability of venlafaxine or its active metabolite. On the basis of mass balance studies, at least 92 % of a single oral dose of venlafaxine is absorbed. The absolute bioavailability is about 45 % and plasma protein binding is approximately 30 %. Venlafaxine and its active metabolite, ODV have an elimination half-life (T½) of 5±2 and 11±2 hours, respectively.
Administration of the immediate release tablets at a dosage of 75 mg every twelve hours results in a Cmax, of 225 ng/ml and 290 ng/ml for venlafaxine and ODV, respectively. Tmax was 2 hours for venlafaxine and 3 hours for ODV. Administration of the extended release capsules provides a slower rate of absorption but the same extent of absorption compared with immediate release tablets. A 150 mg dose of the extended release capsules results in a lower Cmax (150 ng/ml for venlafaxine and 260 ng/ml for ODV) than for immediate release venlafaxine tablets. Tmax for the extended release capsules was 5.5 hours and 9 hours for venlafaxine and ODV, respectively. Steady-state concentrations of venlafaxine and ODV are attained within three days of oral multiple dose therapy. Plasma concentrations are altered by hepatic and renal impairment but unaltered by gender and age. Poor metabolizers, i.e. patients with low CYP2D6 levels have increased levels of venlafaxine and reduced levels of ODV than extensive (“normal”) metabolizers. However, there is no need for dosage adjustment because of similar areas under the curve (AUCs). The commercially available product is a racemic mixture of the (+) and (−) enantiomers of venlafaxine. All the metabolites are racemic.
Numerous techniques exist in the prior art for preparing sustained or controlled release pharmaceutical formulations. Controlled release means or delivery devices that are well known to those of ordinary skill in the art, are described, for example in U.S. Pat. Nos. 3,845,770; 3,916,899; 3,536,809; 3,598,123; 4,008,719; 5,674,533; 5,059,595; 5,591,767; 5,120,548; 5,073,543; 5,354,556; 5,733,566 and 6,403,120 the disclosures of which are incorporated herein by reference.
U.S. Pat. No. 6,048,547 discloses a sustained-release venlafaxine hydrochloride pharmaceutical composition where venlafaxine and microcrystalline cellulose are combined with polyethylene oxide (PEO) and compressed into tablets.
Controlled release of the commercially available extended release venlafaxine hydrochloride capsules (EFFEXOR®) is achieved by diffusion through the coating membrane on the spheroids and is not pH dependent. EFFEXOR® XR is available in a once daily dosage form of venlafaxine which contains cellulose, ethylcellulose, gelatin, hydroxypropyl methylcellulose, iron oxide, and titanium dioxide.
The need also exists for a simply and economically produced pharmaceutical preparation which provides a pulsatile delivery system (immediate release followed by sustained release) which attains peak plasma levels, in the manner of an immediate release product, i.e earlier than a controlled release formulation, followed by sustained release over 24 hours. This results in allowing greater flexibility in designing sustained release profiles and providing improved plasma levels wherein the maximum plasma concentration (Cmax) can be substantially reduced without a concomitant reduction in the area under the curve (AUC) and without prolongation of the time in which the maximum plasma concentration is obtained (Tmax). Such a delivery dosage form has a practical application, and it represents a valuable contribution to the pharmaceutical arts. The present invention provides such a composition, and offers an efficient and cost effective method of preparation.
The present invention was created through efforts to solve the above problems, as well as other problems, and provides a superior pellet formulation of venlafaxine, its pharmaceutically acceptable salts and its active metabolite o-desmethyl venlafaxine (ODV).
Accordingly, it is an object of this invention to provide an oral pharmaceutical formulation of venlafaxine hydrochloride or its active metabolite (ODV) suitable for once daily administration that obtains its maximum plasma levels in less than 4 hours.
It is a further object of the present invention to provide a once a day pharmaceutical formulation that will provide 24 hour control of symptoms of depression or Generalized Anxiety Disorder.
The present invention relates to a new sustained release venlafaxine or its active metabolite pharmaceutical composition producing novel blood plasma levels which is not disclosed in, not rendered obvious by, previous patents nor elsewhere in the art. Other objects, features and advantages of the invention are not taught in the prior art, but will be more apparent to those versed in the art from the following specification, taken in conjunction with the drawings.